changes in milk protein with heat
Posted 18 June 2010 - 05:24 AM
Question: Does anyone know the specific temperature that changes the milk proteins--I think the term is "denaturing"? Based on our experience, I would think it would have to be above 100 degrees (to account for the white chocolate reaction). But what is the minimum temperature that it would need to be held at. Obviously, I'd rather investigate this issue from the comfort of my computer than from the inside of an ER-- don't really want to turn the boy into a guinea pig in my kitchen. As we adjust to our new dining possibilities, I'm just trying to figure out how "cooked" is "cooked"?
Posted 18 June 2010 - 07:32 AM
Interesting ... they think it has to do with the way the proteins change shape as the milk is heated such that the immune systems do not recognize them as an allergen. If you do find out what temp/time combination is essential I too would be interested in hearing....!
Posted 18 June 2010 - 08:40 AM
The most numerous whey protein coagulates around 172 F, but thats about all the info I can find/remember...just re read the milk section in on food and cooking last week. Thanks Harold McGee!
Posted 18 June 2010 - 09:03 AM
At an empirical level, I've taken this to mean heating to almost but not quite boiling, but sufficiently hot that on cooling, a skin forms.
I believe the skin is a protein product ...
Wikipedia suggests that the temperature for this is 82C - but that seems to be a conversion of the round number of 180F - so don't take it as being precise!
However, I'd suspect that what is happening is enzymic, rather than pure thermal destruction of one or more specific proteins - that's called 'burnt milk'!
And the thing about enzymic reactions is that they don't happen instantly - they take a variable amount of time at different temperatures.
So, just as with pasteurisation, you'd have to specify a time at whatever temperature ...
I suspect that any taste/mouthfeel changes may be associated with the transformations that are desired - and hence unavoidable.
Any experimentation at lower temperatures is going to involve longer, possibly much longer, holding times. And here I'm thinking of sous vide methodologies ...
But, hey, if you have a milk-treatment protocol (heat pan to boiling point and then cool naturally) that works for you, then exploit it!
Posted 18 June 2010 - 04:54 PM
And I also think the structure of the protein changes via heat to something that isn't recognized as an invader. It's also interesting that some cheeses, especially hard cheeses seem to be less problematic for my son. We had been humming right along on a dairy-free diet for him for years until last summer when we discovered that he had actually eaten some sundried tomato pesto that had parmesan in it, and he didn't have a reaction. That got us wondering if had outgrown his allergy over the years. We had him tested-- both skin-prick and blood tests-- which indicated he was still wildly allergic. I pressed the issue with our allergist and she finally allowed us to do an oral challenge in her office (as opposed to the ER with an IV all set up.) And lo, and behold, he was able to eat two muffins made with milk.
I know cheese making involves heating the milk to various temperatures, but I'm also wondering if the aging process of hard cheeses also helps to break the protein down. I wish there was some specific answer to these qustions, but I have a feeling that it will all depend on the milk and what it's mixed with as well as whatever is happening in my son's body at the time.
As an aside, he had his first slice of cheese pizza tonight and had no ill effects-- which led to another slice, and then another, and then another! For a 13 year old boy, the ability to go out to pizza with his friends is worthy of doing a huge happy dance in our family!
Posted 20 June 2010 - 07:34 AM
Do a search on the page for 'Whey Proteins.' It's that section where he talks about lactoglobulin, the most abundant whey protein, which happens to be denatured by heat at 172 deg. f. He also talks about acid coagulation and whey drainoff processing for a 'true' ricotta.
White chocolate is made with whole milk powder. Whole milk powder, as far as I know, is made using a spray process and probably isn't exposed to lactoglobulin denaturing temps.
You might want to pick up some powdered casein (bodybuilding site) and some powdered whey protein isolate and, under your doctor's supervision, test him for both. Again, like milk powder I believe they're a spray dried process. That might allow you to narrow it down to the whey.
Posted 20 June 2010 - 07:44 AM